Method and apparatus for washing wood chips

ABSTRACT

Wood chips including foreign substances are made to naturally sink in a washing tank. While the floating chips are taken out from the tank, the sinking chips and the foreign substances are separated by a submerged screen so that only the small sand may fall through the screen. The sinking chips and other foreign substances are brought into a selection tube in which an upward stream is provided. By the upward stream, the wood chips are moved up for recovery and only the foreign substances sink through the stream.

United States Patent 1191 Morimasa 1 Jan. 2, 1973 54 METHOD AND APPARATUS FOR 3,279,597 10/1966 Reinhall ..2o9 161 x WASHING WOOD CHIPS 3,308,951 3/1967 Evans ..209 158 inventor! Mm'im'sa, Kul'e-Shi, FOREIGN PATENTS OR APPLICATIONS Hiroshima Pref.,.lapan 699,132 10/1953 Great Brltam ..209/158 [73] Assignee: Toyo Pulp Co., Ltd., Tokyo, Japan Primary Examiner--Frank W. Lutter [22] Filed 1970 Assistant ExaminerRalph J. Hill [21] Appl. No.: 71,622 Attorney-James E. Armstrong and Ronald S. Cornell 521 US. 01. ..209/3, 209/17, 209/158, 5 ABSTRACT 209/160 Wood chips including foreign substances are made to [51] Int. Cl. 7/00 naturally ink in a washing tank while the floating Field of Search 309/3, 171465, 153-161, chips are taken out from the tank, the sinking chips 140, 141 and the foreign substances are separated by a submerged screen so that only the small sand may fall [56] Reffl Cited through the screen. The sinking chips and other foreign substances are brought into a selection tube in UNITED STATES PATENTS which an upward stream is provided. By the upward 1,544,999 7/1925 Lequeux ..209/454 X stream, the wood chips are moved up for recovery and 2.357.050 10/1953 Nebel t 9/ 159 only the foreign substances sink through the stream. 3,042,198 7/1962 Slavich ..209/44 3,243,039 3/1966 Harshberger ..209/10 X 9 Claims, 3 Drawing Figures PATENTEDJAH 2 ma SHEET 1 BF 3 METHOD AND APPARATUS FOR WASHING WOOD CHIPS ing out the method.

The conventionally known types of washer of the tank and flume type are represented by the washer disclosed in US. Pat. No. 3,243,039. In such washers it has been difficult to recover the sunken chips because of the fact that such chips easily fall into the bottom of the tank and flume. The sunken chips are removed together with foreign substances. Since to 30 percent of all chips sink because of the displacement of hollow spaces in the chips by water, it has required great cost and timeto separate the sunken chips from the removed foreign substances. When dried wood chips are thrown into the water, they float. However, after the passage of a certain time at least some of the wood chips sink gradually and separately in the water, because water enters into a plurality of holes in the chips. For example, the Douglas Fir on the west coast of the U.S.A. has about 0.44 in specific gravity when the material is dried completely. However, its true specific gravity is about 1.05 when the holes in the chips are crushed. Therefore, the wood chips containing water sink.

Under the above described disposition of the conventional wood chip washer, a new or improved washer providing a simple means for removing the sunken chips from the foreign substances has been long needed.

Accordingly, it is a primary object of the present invention to provide a method of washing wood chips, including a step of removing the sunken chips from the foreign substances.

Another object of the present invention is to provide a method of washing wood chips in which the sand is easily removed from the wood chips.

Still another object of the present invention is to provide a method of washing wood chips by which the foreign substances are completely removed and separated.

A further object of the present invention is to provide a method of washing wood chips in which the fine fibers are recovered together with the wood chips.

A still further important object of the present invention is to provide an apparatus for carrying out. the foregoing method.

Other objects, features and advantages of the present invention will be readily apparent to those skilled in the art from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a vertical sectional view of an embodiment of the washing apparatus for carrying out the method of washing wood chips in accordance with the present invention,

FIG. 2 is a top view of the washing apparatus shown in FIG. 1, and

FIG. 3 is a graphic illustration showing the sinking speed of the wood chips, saw dust and sand as a function of particle size thereof.

In order to better understand the method of the invention and the construction of the apparatus for carrying out the method, a brief summary of the invention will be helpful.

The methods according to the present invention are performed as follows; in the first stage the chips, while falling into a washing tank, are subjected to high pressure jets of water which separate them from each other and cause them to flow along the scraper in a current of water and washing them by repeated sinking action to free the metal, gravel, sand, and other foreign substances and finally discharges said chips by floating them through a gate.

In the second stage the sunken chips and any foreign materials, while falling into the bottom of washing tank, are subjected a submerged screen. plate which removes the fine sands and discharges them into an upward flow pipe which separates them from the chips and any other foreign materials by the natural difference of sinking speed. A bottom scraper is arranged to scrape the surface of the submerged screen to remove any sunken materials.

In the third stage, the floating chips along with the sunken chips which rise through the upward flow pipe and water are discharged onto a vibrating screen which performs a washing and dehydrating action by strong agitation.

The average size of the wood chips is 20 to 25 mm and the chips include 5 to 7 percent fine particles of a size of not more than 9 mm. The saw dust which has received attention recently as material for pulp, has a size mainly of not more than 9 mm, and 60 to percent of the saw dust has a size of 1.2 to 4 mm. Therefore, in accordance with the conventional method of washing wood chips, a large amount of saw dust is mingled in the removed stones and sands together with the sinking chips. In view of the foregoing fact, in the method of the present invention there is provided a constant upward stream from beneath the submerged screen at a speed of around 4 cm/sec which is equal to the maximum of the free sinking terminal speed so asto prevent the saw dust from sinking and make only the sand sink.

The terminal speed of the free sinking of the saw dust, chips, and sand is shown in FIG. 3 in which the ordinate represents the speed (cm/sec) and the abscissa represents the size of the particles (mm). As read from the graph in FIG. 3, the free sinking speed of the sand is from about 4.5 to cm/sec in the range of 0.1 to 100 mm of the diameter, and the sinking speed of the wood chips is from about 12 to 25 cm/sec in the case where the flat wood chips of the size 20 to 25 mm are made to sink in the direction of their flatness, and from about 4.2 to 8.8 cm/sec in the case where the wood chips are made to sink in the direction normal to the flat face thereof. The sinking speed of the wood chips depends on the angle of sinking due to the flat shape thereof more than the size. On the other hand the free sinking speed of the wood saw dust does not depend on the angle of sinking since it is of a granular shape. The free sinking speed of the saw dust is from about 1.7 to 3.5 cm/sec within the range of 0.5 to 8 mm of the size thereof and is not effected by the size in the range over 3 mm.

The relation between the free sinking speeds of the saw dust, wood chips and sand, and the speed of the upward water stream in the selection tube, diameter of the slit or hole of the submerged screen and the speed of the upward stream through the slits or hole of the submerged screen is represented as follows:

F I] 2 Cmar (I) Smin 2 VB 2 SDmmr where V, free sinking speed of the sand V free sinking speed of the saw dust V free sinking speed of the wood chip V speed of the upward water stream in the selection tube V,, speed of the upward water stream through the slits or holes of the submerged screen V free sinking speed of the sand of the size equivalent to the size (b of the holes or slits of the submerged screen 41 size of the holes or width of the slits of the submerged screen L size of the chip In other words, the size of the sand particles removed by the submerged screen is limited by the size 4; of the holes of the screen and in the case where the size of the holes in the screen is 10 mm for instance, the free sinking speed V, of the sand of the size corresponding to the size of the holes is about 35 cm/sec. Accordingly, the speed of the upward water stream in the selection tube V is required to be, e.g., 30 cm/sec which is under the speed 35 cm/sec and is also required to be higher than the maximum speed V of the free sinking speed of the wood chips, about 25 cm/sec.

The speed of the upward water stream through the slits or holes of the submerged screen V should be ofa degree to fulfil the condition which permits the sand to sink through the slits or holes of the submerged screen, but prevent the chips and saw dust from sinking therethrough. For instance, in the case where the speed of the upward water stream through the slits or holes is 4 cm/sec, this speed satisfies the condition as set forth above in that it is smaller than the minimum V of the free sinking speed of the sand or 4.5 cm/sec. (The sand of a size smaller than 0.1 mm is considered negligible since it does not have any influence.) and is larger than the maximum VSDMI of the free sinking speed of the saw dust or 3.5 cm/sec and chips which size range is 20 to 25 mm and thus can not pass through mm holes.

Now the method of the present invention will be described in detail referring to the drawing showing an embodiment of the apparatus for carrying out the method of the invention. A conical washing tank 3 having a wall inclined by predetermined gradient is partitioned by a submerged screen 14 into a lower second sinking tank 16 and an upper first sinking tank and the first sinking tank 15 which is further partitioned with a partition plate 10 into a first washing portion and a second washing portion. The partition plate 10 is connected in a secured fashion to washing tank 3.

A discharge channel 9 having a discharging shoot 1 l is connected to the outer periphery of the washing tank 3. At the central portion of the washing tank 3 is provided a stirrer shaft 5 and a stirrer driving motor 4. On the surface of the water in the washing tank 3 are disposed inner blades of the washing scraper 6, outer blades of the washing scraper 7 and discharge scraper 8. Another scraper 12 is mounted at the lower end of the stirrer shaft 5 so that the scraper 12 may sweep on the submerged screen 14 in the washing tank 3. At the bottom of the second sinking tank 16 is disposed a sand trap 17 having sluice valves 13 at the top and bottom thereof. A metal and stone trap 19 is connected with the portion of the tank 3 just above the submerged screen 14 through a discharging tube 18. The top central portion of the metal and stone trap 19 is connected with the discharge channel 9 through a selection tube 20.

Under the discharge shoot 11 is disposed a vibrating screen 21, under which is disposed a screen pit 23 with a circulating pump 24. The discharge stream from the circulating pump 24 is guided to the metal and stone trap 19 and the nozzles 26 and 27 through stream pipe 25.

Above the first washing portion of the washing tank 3 within the partition 10 are disposed a chip supplying conveyer 1 and a supply shoot 2. The chips supplied from the chip supplying conveyer 1 are introduced into the first washing portion in the partition 10 in the washing tank 3 through the supply shoot 2. The chips are introduced deep into the tank 3 by the jet from the nozzle 26 of the circulating stream. in the first washing portion within the partition 10 of the washing tank 3, the chips are sufficiently stirred by the jet from the nozzle 26 and by the inner blades 6 of the washing scraper so that almost all the stones, metals and sand in the chips sink into the water and the chips sufficiently washed are moved to the second washing portion in the washing tank beyond the partition 10. The chips in the second washing portion are sufficiently stirred by the outer blades 7 of a washing scraper and the most residual foreign substances sink and the washed chips are discharged by the discharging scraper 8 out of the washing tank 3. The discharged chips are moved into the discharging channel 9 and guided to the vibrating screen 21 through the discharging shoot 11 together with the secondary washed chips rising up through the selection tube 20. The chips are discharged onto the discharging conveyor 22 disposed under the vibrating screen 21. The chips are drained by the vibration of the vibrating screen 21.

On the other hand, the foreign substances and the sunken chips in the first and second washing portions sink down to the submerged screen 14. On the submerged screen 14 between the upper first sinking tank 15 and the lower second sinking tank 16, the saw dust is prevented from sinking down into the second sinking tank 16 by the upward stream of the speed of around 4 cm/sec made by the nozzle 27 disposed in the second sinking tank 16. Thus, only the small sand (under than 10 mm Size) which is able to sink through the slits or holes of the submerged screen of the size of about 10 mm sink further into the second sinking tank 16 and are discharged into the sand trap 17 through the sluice valve 13. The stones, metals, minerals, sunken chips and the like which are not able to sink through the submerged screen 14 drop into the discharging tube 18 by the operation of the scraper 12. The foreign substances and the sunk chips guided into the discharging tube 18 are subject to the upward stream of the speed of 5 to 35 cm/sec from the metal and stone trap 19 through the selection tube 20, and the chips (the sinking speed thereof is 5 to 25 cm/sec) having a large surface area and small specific gravity are moved up through the selection tube being guided by the upward stream and the stones and metals and minerals (the sinking speed thereof is over than 35 cm/sec) having a large specific gravity with respect to the surface area thereof sink down into the stone and metal trap 19. The wood chips moved up through the selection tube 20 by the upward stream having a larger speed than the sinking speed of said wood chips are brought into the discharging channel 9 so that the wood chips may be discharged into the vibrating screen and put onto the discharging conveyer 22 after draining.

The water from the drained chips on the vibrating screen 21 drops into the water tank 23 and is used in the circulation system by the circulating pump 24. The water is brought into the stone and metal trap 19 and nozzle 26 through the water pipes 25 and 27.

One of the Swedish Methods and apparatus for washing the wood chips and removing the foreign substances is disclosed in the Japanese Pat. publication No. 5521/65. In this method and apparatus, large amounts of the water and compressed air are feed from the bottom of the separating tank so as to prevent the chips from sinking due to the strong agitation, and foreign substances are discharged from the bottom of the separating tank. There has been a disadvantage in that method and apparatus in the selected chips often include foreign substances of comparatively small size thus requiring the selected chips to be again washed with a large amount of water in shower form, and also requiring extraordinary equipment such as a centrifugal separator for recovering the chip dust from the foreign substances in the shower. The above disadvantage is due to the fact that the separating means in the Swedish type wood chip washer is provided with a means for introducing water and air from the bottom of the separator for preventing the chips from sinking due to the strong agitation and a means for removing the foreign substances from the bottom of the separator.

In accordance with the present invention, the above described defects of the Swedish type wood chip washer are completely eliminated by permitting the chips to naturally sink in a washing tank so that the floating chips may be completely separated from the foreign substances and the sinking chips. Also in the present invention, the fine particles of foreign substances are removed through a submerged screen, and the sinking chips and the foreign substances of comparatively large size are discharged out of the tank through a discharging pipe into a selection tube, in which only the sinking chips are moved upward with a vertical stream of water and recovered while the foreign substances sink down and are discharged into a trap.

As briefly stated hereinbefore, the present invention has such advantages as follows in comparison with the prior art;

1. Recovery of the sinking chips: In the prior art chip washer, there has been no method of separating the sinking chips (10 to 30 percent of the sinking chips are included though depending on chip moisture) from the stones, metals and the like, and it has taken a lot of money and time for selecting the sunken chips included in the foreign substances have sunk after all the substances. 0n the other hand, in accordance with the present invention, the sinking chips are capable of being separated from the foreign substances by placing the substances in a upward stream and utilizing the natural differences in the specific gravities, surface area and sinkingspeed between the foreign substances and the sinking chips.

2. Separation of the sand: In the prior art chip washer, it has been very difficult to separate the sand from the wood chips. In the present invention, the sand is completely removed from the wood chips by washing the wood chips in the washing tank using a scraper repeatedly and further by means of a submerged screen.

3. Complete washing of the wood chips: In the prior art wood chip washer, the washing of the wood chips and removal of the sand have been incomplete since the chips have been washed only by a shower at most. In the present invention, the washing tank is partitioned into two sinking tanks and the wood chips are sufficiently washed repeatedly in a second sinking tank and not only the sand but also other foreign substances such as mud and the like are completely removed from the wood chips.

4. Recovery of the fine fiber: In the prior art wood chip washer, the fine fibers have been removed together with the foreign substances by the shower. Since the fine fibers are able to be produced into pulp, the removal of the tine fibers has been a loss of the material for pulp. In the present invention, the fine fibers are also recovered together with the sinking chips to reduce the loss of thematerial for pulp. Accordingly, even in the case where the material mainly containing fine fibers such as saw dust is washed, the material to be used for pulp is prevented from sinking by the upward stream under the submerged screen.

What is claimed is:

l. A method of washing sand and foreign matter from material composed of wood. chips and saw dust with said sand and said foreign matter mixed therein, and said method comprising; introducing said material into a washing tank with a screen with predetermined mesh size openings to allow only sand and saw dust to pass therethrough in a lower portion thereof, disas sociating said material with a jet stream of water as said material is introduced, passing a flow of water upwardly through said screen at a velocity sufficient to prevent passage of saw dust through said screen and sufficient to prevent sinking at least a portion of the wood chips, but insufficient to prevent the sinking of sand, stirring said material in said tank, discharging floating wood chips from the top of said tank, moving material which collects on said screen into an adjoining selection tube by mechanical means, passing a flow of water upwardly in said selection tube at a velocity suffcient to carry any wood chips and saw dust upwardly therein while allowing foreign matter to sink therein, discharging wood chips and saw dust from the top of said selection tube, and collecting sand and foreign matter in the bottoms of said washing tank and said selection tube respectively.

2. A method of washing sand and foreign matter from material composed of wood chips and saw dust according to claim 1, wherein sinking wood chips are collected on said screen and all material discharged from the top of said tank is collected on a vibrating screen and the water drained therefrom by vibration.

3. A method of washing sand and foreign matter from material composed of wood chips and saw dust according to claim 1, wherein the drained water from said materials is collected in a container and recycled by a pump as the source for said jet stream and said flow of water through said screen and said selection tube.

4. Apparatus for washing wood chips comprising a washing tank, a scraper mounted by a shaft to the upper portion of the washing tank for stirring and discharging the chips and connected to a driving means, a submerged screen disposed at the lower portion of said washing tank, a discharge tube connected to the side of said washing tank at the portion just above said submerged screen, a selection tube connected with the end of said discharge tube, the upper end of said selection tube being connected with a discharge channel, the lower end of said selection tube being connected to a foreign substances trap, and a water tank disposed below said discharge channel and a pump connected to said water tank for drawing water therefrom and connecting means extending from said pump to the top of said tank, the lower end of said selection tube below the point of connection with the discharging tube and the bottom of said washing tank below the submerged screen for introducing water to each said location.

5. Apparatus for washing wood chips according to claim 4, wherein a trap is connected to the lower end of said washing tank beneath said submerged screen to receive sand particles and the like.

6. Apparatus for washing wood chips according to claim 4, wherein a vibrating screen is disposed beneath said discharge channel and above said water tank to collect and drain the materials discharged.

7. Apparatus for washing wood chips according to claim 4, wherein said washing tank is partitioned into a first washing portion and a second washing portion by a plate disposed in spaced relation beneath the scraper and around the circumference of said shaft and secured to said washing tank, and wherein second washing portion contains said submerged screen.

8. Apparatus for washing wood chips according to claim 4, wherein said scraper is composed of inner blades, outer blades and discharge blades disposed in a sequentially connective relationship, and a second scraper is mounted at the lower end of said shaft and above said submerged screen for scraping said screen.

9. Apparatus for washing wood chips according to claim 4, wherein a supply means is provided above the top of said washing tank for introducing chips thereint0. 

1. A method of washIng sand and foreign matter from material composed of wood chips and saw dust with said sand and said foreign matter mixed therein, and said method comprising; introducing said material into a washing tank with a screen with predetermined mesh size openings to allow only sand and saw dust to pass therethrough in a lower portion thereof, disassociating said material with a jet stream of water as said material is introduced, passing a flow of water upwardly through said screen at a velocity sufficient to prevent passage of saw dust through said screen and sufficient to prevent sinking at least a portion of the wood chips, but insufficient to prevent the sinking of sand, stirring said material in said tank, discharging floating wood chips from the top of said tank, moving material which collects on said screen into an adjoining selection tube by mechanical means, passing a flow of water upwardly in said selection tube at a velocity sufficient to carry any wood chips and saw dust upwardly therein while allowing foreign matter to sink therein, discharging wood chips and saw dust from the top of said selection tube, and collecting sand and foreign matter in the bottoms of said washing tank and said selection tube respectively.
 2. A method of washing sand and foreign matter from material composed of wood chips and saw dust according to claim 1, wherein sinking wood chips are collected on said screen and all material discharged from the top of said tank is collected on a vibrating screen and the water drained therefrom by vibration.
 3. A method of washing sand and foreign matter from material composed of wood chips and saw dust according to claim 1, wherein the drained water from said materials is collected in a container and recycled by a pump as the source for said jet stream and said flow of water through said screen and said selection tube.
 4. Apparatus for washing wood chips comprising a washing tank, a scraper mounted by a shaft to the upper portion of the washing tank for stirring and discharging the chips and connected to a driving means, a submerged screen disposed at the lower portion of said washing tank, a discharge tube connected to the side of said washing tank at the portion just above said submerged screen, a selection tube connected with the end of said discharge tube, the upper end of said selection tube being connected with a discharge channel, the lower end of said selection tube being connected to a foreign substances trap, and a water tank disposed below said discharge channel and a pump connected to said water tank for drawing water therefrom and connecting means extending from said pump to the top of said tank, the lower end of said selection tube below the point of connection with the discharging tube and the bottom of said washing tank below the submerged screen for introducing water to each said location.
 5. Apparatus for washing wood chips according to claim 4, wherein a trap is connected to the lower end of said washing tank beneath said submerged screen to receive sand particles and the like.
 6. Apparatus for washing wood chips according to claim 4, wherein a vibrating screen is disposed beneath said discharge channel and above said water tank to collect and drain the materials discharged.
 7. Apparatus for washing wood chips according to claim 4, wherein said washing tank is partitioned into a first washing portion and a second washing portion by a plate disposed in spaced relation beneath the scraper and around the circumference of said shaft and secured to said washing tank, and wherein second washing portion contains said submerged screen.
 8. Apparatus for washing wood chips according to claim 4, wherein said scraper is composed of inner blades, outer blades and discharge blades disposed in a sequentially connective relationship, and a second scraper is mounted at the lower end of said shaft and above said submerged screen for scraping said screen.
 9. Apparatus for washing wood chips according to claim 4, wherein a supply meanS is provided above the top of said washing tank for introducing chips thereinto. 